In multicellular animals, growth, proliferation and differentiation are regulated by extracellular signals. Genetic studies of the Drosophila eye have identified signals that drive a wave of differentiation across the retinal epithelium, and regulate cell proliferation and survival processes that are closely associated with differentiating photoreceptor cells. Most extracellular signaling pathways do not act independently but often interact antagonistically, synergistically or redundantly. Future studies will determine what extracellular signals control the patterning of the retina prior to differentiation by taking a systematic approach to eliminate the response to Hh, Dpp, Wg, N and EGF receptor pathways. Genetic mosaic analysis of mutant genes affecting each pathway will be compared with genotypes where one or more signaling pathways function. Extracellular signals arrest the cell cycle prior to the onset of neurogenesis, and the function of this arrest will be assessed through study of the mutant genotypes that prevent it. The mechanisms of selected gene targets of extracellular signals in proliferation, differentiation, and survival will be elucidated. These studies will take a systematic approach to the regulation of the retina by extracellular signals.